1. Field of the Invention
The invention relates to a planet roller speed changer.
2. Description of the Related Art
As described in Japanese Patent Application Publication No. 2003-161351 (JP 2003-161351 A), there is a conventional planet roller speed changer (traction drive) in which each of cylindrical planet rollers is rotatably supported in a loosely fitted state by a pin that passes through the inner periphery of the planet roller and that protrudes from a carrier. A cylindrical bushing is fixedly fitted onto the outer periphery of each pin. Because each planet roller is in the loosely fitted state, there is a clearance between the inner periphery of the planet roller and the outer periphery of a corresponding one of the bushings.
For example, the planet roller speed changer is mounted transversely in an apparatus such as an image forming apparatus (i.e., mounted in a state where an input shaft and an output shaft of the planet roller speed changer extend along the horizontal direction) in some cases. In such a mounted state, the carrier may be displaced downward from a prescribed position under its own weight. As a result, there sometimes occurs a state where the center of rotation of the carrier and the center of revolutions of the planet rollers supported in the loosely fitted state by the pins of the carrier do not coincide with each other, that is, a state where the center of rotation of the carrier is misaligned with the center of revolutions of the planet rollers.
In this case, if the outer peripheral face of the bushing contacts the input shaft side-portion of the inner periphery of the planet roller due to the misalignment of the center of rotation of the carrier with the center of revolutions of the planet rollers, the revolution of the pin may be promoted. Due to a change in the relative position between the planet roller and the pin caused by the misalignment of the center of rotation of the carrier with the center of revolutions of the planet rollers, rotation of the carrier is advanced or delayed when the output shaft is rotating. When the outer peripheral face of the bushing contacts the input shaft side-portion of the inner periphery of the planet roller, the rotation of the carrier is advanced or delayed significantly. As a result, large rotational fluctuations may occur in the planet roller speed changer.